Semiconductor devices are found in many products in the fields of entertainment, communications, networks, computers, and household markets. Semiconductor devices are also found in military, aviation, automotive, industrial controllers, and office equipment. The semiconductor devices perform a variety of electrical functions necessary for each of these applications.
The manufacture of semiconductor devices involves formation of a wafer having a plurality of die. Each semiconductor die contains hundreds or thousands of transistors and other active and passive devices performing a variety of electrical functions. For a given wafer, each die from the wafer typically performs the same electrical function. Front-end manufacturing generally refers to formation of the semiconductor devices on the wafer. The finished wafer has an active side containing the transistors and other active and passive components. Back-end manufacturing refers to cutting or singulating the finished wafer into the individual die and then packaging the die for structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce a package suitable for faster, reliable, smaller, and higher-density integrated circuits (IC) at lower cost. Flip chip packages or wafer level chip scale packages (WLCSP) are ideally suited for ICs demanding high speed, high density, and greater pin count. Flip chip style packaging involves mounting the active side of the die face down toward a chip carrier substrate or printed circuit board (PCB). The electrical and mechanical interconnect between the active devices on the die and conduction tracks on the carrier substrate is achieved through a solder bump structure comprising a large number of conductive solder bumps or balls. The solder bumps are formed by a reflow process applied to solder material deposited on contact pads, which are disposed on the semiconductor substrate. The solder bumps are then soldered to the carrier substrate. The flip chip semiconductor package provides a short electrical conduction path from the active devices on the die to the carrier substrate in order to reduce signal propagation, lower capacitance, and achieve overall better circuit performance.
In high frequency applications, such as radio frequency (RF) wireless communications, integrated passive devices (IPDs) are often contained within the semiconductor device. Examples of IPDs include resistors, capacitors, and inductors. A typical RF system requires multiple IPDs in one or more semiconductor packages to perform the necessary electrical functions.
In the design phase, it is often desirable to analyze a high frequency passive circuit to determine its characteristic parameters, i.e., impedance (Z), admittance (Y), hybrid (H), inverse hybrid (G), and scattering transmission (T) parameters. One common circuit approach is to perform a two-port network analysis. The passive circuit is evaluated as a black box with measurements taken at its two ports. The two-port analysis provides a set of distinctive properties that define its electrical behavior without considering the specific circuit schematic or individual components or their values. Any linear circuit with four terminals can be transformed into a two-port network provided that it does not contain an independent excitation source.
As one simplified example, FIG. 1 shows a two-terminal inductor and capacitor (LC) resonator 10. Resonator 10 exhibits resonance or oscillations at its natural frequency, i.e., the circuit generates higher amplitude oscillations at the resonant frequency than other frequencies. The resonator typically reacts based on physical, dielectric, or electromagnetic properties of the device. Inductor 12 and capacitor 14 are electrically coupled in series. The first port is designated by terminals 16 and 18 and the second port is designated by terminals 20 and 22. The series LC circuit represents the electrical functionality of the resonator.
During the manufacturing and testing phase, it is necessary to confirm the functional operation of resonator 10. The circuit board or substrate contains test pads arranged in accordance with terminals 16-22 of FIG. 1. The two-port network performs a series measurement of resonator 10 as the LC circuit is in series with terminals 16 and 20. A plurality of probes from a testing system is placed on the test pads to apply a voltage or inject a current into resonator 10. The test probes measure the frequency response and quality factor Q of resonator 10 with the intent of confirming that the manufactured circuit complies with the design specifications.
Unfortunately, the test probes have a series resistance which affects the test measurements. The system is measuring the reactance of inductor 12 and capacitor 14 in combination with the series resistance of the test probes. The test probe resistance introduces errors into the test system and alters the test results.